Restless leg syndrome (RLS) is a common sensory-motor disorder that has a significant negative impact on the quality of life for estimated 8 million Americans. Low brain iron, despite the absence of currently existing systemic iron deficiency, appears to be an important part of the pathology and an important endophenotype of the disease identifiable with special MRI techniques. One hypothesis is that an initial, early exposure to iron deficiency (ID) leads to a cell protective response, which, despite the normalization of peripheral iron status, can have a long-term effect on cellular iron homeostasis that sensitive the system to later challenges. Epigenetic processes provide a mechanism by which environmental factor can influence later life genetic. Thus early exposure to ID condition may lead to epigenetic changes that set up the risk of developing RLS with later exposure to environmental factors (e.g., pregnancy, iron deficiency, chronic renal failure, age-related factors) leading to the phenotypic expression of the underlying genotype. RLS also shows a dominant inheritance pattern with children from affected mothers having a higher risk than from affected fathers, yet no dominant or co-dominant gene(s) has been found in GWAS and family studies. In utero exposure to ID with consequential epigenetic changes may help explain this heritability nature in RLS. Our primary interest is to identify RLS-relevant epigenetic factors in readily accessible tissues, so later studies can use them as biomarkers of disease risk and possible indicators of RLS biology and associated medical conditions. CpG methylation changes in lymphocytes, which have previously been shown to have cellular changes similar to that seen in RLS autopsy brains, will be used. MRI will be used to measure iron concentrations in the substantia nigra (SN), which is a well-accepted brain-related endophenotype of the disease. ID is the most significant and well-recognized environmental factor associated with triggering RLS symptoms in adults. The prevalence of RLS in the most extreme ID conditions (iron deficiency anemia (IDA)) is 30-40% compared to 5% prevalence of RLS in the general population. A severe iron deficient condition will be used to delineate two groups with a high degree of discriminative ability to identify disease-relevant or disease-irrelevant epigenetic biomarkers. Epigenetic changes, unlike genetic change, are preventable and in some cases reversible. Preventing ID, therefore, could potentially have the significant impact on RLS development. If a genetic-epigenetic interaction is identified, then screening for the genetic risk component and applying preventive steps in this group could dramatic change the public health risk of RLS. A similar option may be indicated for those with a family history of RLS. The findings would clearly impact the future direction of research in RLS with more of emphasis on public health risk and prevention of iron deficiency.